16

Data Visualization and Cartography Basics

Introduction to Cartography

  • Cartography: The study, practice, and art of making maps.

  • Purpose: To transmit spatial information effectively to the map reader.

  • Key considerations in cartography include the intended message and the audience.

Goals of Different Groups in Cartography

  1. County Chamber of Commerce: Show the shortest and least costly route for a connector while focusing on property values.

  2. Community Group: Argues the connector will negatively affect the African American community.

  3. Historical Preservation Group: Indicates that historical properties will be adversely affected by the connector.

  4. Business Association: Posits that the road will divert traffic away from businesses in the area.

  5. Property and Historical Context: Use of maps to highlight community issues, historical significance, and economic growth.

Learning Objectives

By the end of this module, you will be able to:

  • Apply principles of effective map design.

  • Identify key elements of maps: title, legend, scale bar, inset map, etc.

  • Make informed decisions on map symbology for different data types.

  • Understand the principles of layout and visual hierarchy in effective map design.

  • Differentiate between WebGIS and desktop GIS applications.

Cartographic Design Decisions

  • Scale and Extent: Deciding on the area of interest and the appropriate map scale impacts symbology choices (e.g. representing a city as a point vs. an area).

  • Projection: Influences the scale, extent, and purpose of the map.

  • Data to Plot: Choices should focus on thematic data as well as geographical features.

  • Data symbology: shapes, sizes, colors, and patterns

  • Labelling: fonts, size

  • Other map elements: legends, title, north arrow, etc.

  • Spatial configuration of all these elements

Types of Maps

  • Choropleth Map: Uses colors to indicate data distribution across regions (e.g. election results).

  • Dot Density Map: Shows data points (e.g. votes) and their density within populated areas.

  • Proportional Symbol Map: Uses symbols of various sizes to represent data magnitude.

  • Heat Map: Visual representation of data density with color gradients.

Data Symbology

  • Represents different types of data:

    • Discrete Data: Represented with points, lines, areas, colors, or shapes.

    • Continuous Data: Displayed with shading based on data values (e.g. population density).

    • Nominal Data: Best presented with hues or shapes, without implying magnitude differences.

    • Quantitative Data: Illustrated with color scales (light to dark) or graduated symbols.

Color Use in Cartography

  • Color Spaces: Different models for representing color; includes HSV (conceptually the easiest), RGB (for computer vision), CMYK (for printing), and web colors (hex triplets).

  • Components of Color:

    1. Hue: The dominant wavelength (color).

    2. Saturation: Intensity of the hue.

    3. Value: Brightness of the color.

  • Color Considerations: Addressing color blindness and choosing appropriate palettes for qualitative, sequential, and diverging data.

  • Qualitative: Totally different hues. Fixed value and saturation for each “class”. Best for categorical variables. (Different candies)

  • Sequential: Fixed hues. Increasing values and saturation = more/higher data values (light green - fewer trees, dark green - more trees).

  • Diverging: contrasting hues. Diverging saturation/value. Shows departure from a meaningful middle value. (e.g., decreasing rainfall - red, no change - white, increasing rainfall - blue).

  • Two variables, one map (bivariate color scales): combine color scales to show relationships between two variables. Best used when there is a relationship between the two variables.

Color blindness

  • 8% of males and 0.5% of females are colorblind.

  • Most commonly, it makes it impossible to tell red from green.

Map Elements

  • Title: Must be clear and concise, indicating the topic, geographic area, and year.

  • Legend: Explains symbols used on the map, should match displayed data.

  • Scale Bar: Helps users measure distances and understand spatial scale.

  • North Arrow: Indicates direction, included if the map isn't oriented north.

  • Inset Map: Provides geographic context.

  • Sources and Credits: Identifies data source, authorship, and projection used.

Principles of Good Map Design

  • Maximize Data-to-Ink Ratio: Present more data with less unnecessary design.

  • Clear Labeling: Prevents ambiguity and distortion in information.

  • Minimize Non-Essential Elements: Adopt a clean design reducing unnecessary details ("chart junk").

Visual Hierarchy

  • Spatial configuration impacts perception and understanding.

  • Arrange map elements according to their importance and intended message to enhance user comprehension.

Practice and Feedback

  • Map-making is an iterative process requiring practice, feedback, and revision to improve clarity and effectiveness.